Equipment and techniques for invisible seaming of multiple projection displays

ABSTRACT

Apparatus and techniques for enhancing blending characteristics of a composite image formed by multiple projection displays are detailed. Included among the apparatuses and techniques is the use of masks, having complimentary, non-linear edges, between a projection axis and a screen. The masks are used to solve the geometric and photometric issues involved with blending sub-images to form a composite image.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional application Ser.No. 60/215,716 filed on Jul. 3, 2000 and International Application No.PCT/JB01/01175 filed on Jul. 3, 2001 and published in English asInternational Publication No. WO 02/05553 A2 on Jan. 17, 2002, theentire contents of which are incorporated herein by this reference.

FIELD OF THE INVENTION

This invention relates to projection of images and more specifically totechniques and equipment for enhancing the blending characteristics ofcomposite images formed by multiple projection displays.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 5,386,253 to Fielding, incorporated herein in its entiretyby this reference, discusses exemplary projection systems utilizing oneor more spatial light modulators (SLMs). As noted in the Fieldingpatent:

-   -   Spatial light modulator devices include so-called “active        matrix” devices, comprising an array of light modulating        elements, or “light valves,” each of which is controllable by a        control signal (usually an electrical signal) to controllably        reflect or transmit light in accordance with the control signal.        A liquid crystal array is one example of an active matrix        device; another example is the deformable mirror device (DMD)        developed by Texas Instruments . . .        See Fielding, col. 1, II. 13–21. Of course, yet other types of        light “engines,” or sources, and projectors exist, and various        of them may be used in connection with the inventions described        herein.

Regardless of the type of projector used, audiences frequently desire tosee images high in detail and richness and low in objectionableartifacts. High resolution and image quality in particular facilitatessuspension of disbelief of an audience as to the reality of theprojected images. Such quality indeed often is an important factor inthe overall success of the motion picture viewing experience amongtoday's audiences.

Producing these high-resolution images is not without added cost,however. Imax Corporation, for example, the intended assignee of thisapplication, utilizes not only specialized cameras and projectors, butalso seventy millimeter, fifteen perforation film to increase theresolution and quality of projected images. Conventional electronicprojectors (and especially those utilizing SLMs), by contrast, generallycannot supply equivalent resolution in projected images. As well, suchelectronic projectors frequently fail to furnish the dynamic range andoverall brightness of images provided by large-format films. Theynonetheless may desirably (or necessarily) be employed to displaynon-film-based images such as (but not limited to) computer-generatedgraphics or material captured with electronic cameras.

In order to achieve the desired resolution, conventional electronicprojection systems have employed “tiling” techniques. Tiling involvesthe use of multiple projection displays of sub-images that are displayedadjacent to each other to form a composite image. The use of multipleprojection displays allows for greater resolution than is available witha single projection display. The sub-images can be blended inside asingle projector or if multiple projectors are used, the sub-images areblended on the screen. For example, when two projectors are used oneprojector projects a first sub-image on a screen. A second projectorprojects a second sub-image on a screen. The first and second projectorsare positioned such that the first and second sub-images are projectedonto a screen adjacent to each other.

It is difficult to align the projectors exactly and thereforeundesirable seams between the first and second sub-images are oftenapparent to the viewer. To improve the appearance and continuity of thecomposite image, the first and second projectors are conventionallypositioned such that the first image slightly overlaps the second image.Mere overlapping of sub-images typically is insufficient, however, asthe additive intensity of the images in the regions of overlap in somescenes likewise may be noticeable to audiences. General methods ofreducing brightness in these regions typically include adjusting theimages either electronically or optically; the latter method is usuallyimplemented using an opaque or reflective element placed in the beam oflight. Thus, invisible seaming of multiple projectors requires carefulmatching of the displays at the seam area(s), both geometrically andphotometrically.

U.S. Pat. No. 6,017,123 to Bleha et al., incorporated herein in itsentirety by reference, discloses one system and method for blendingsub-images. FIG. 13 of Bleha et al. shows the use of filters and masks,located between the projection lens and the screen, to blend thesub-images. The mask used by Bleha is a knife edged mask. Introducingsimple knife edge masks into the optical path, in front of theprojection lens, generally produces a guassian blurred edge, which whencombined with a complimentary edge on the other projection lens, andprecisely aligned so that the sum of their black levels remains asconstant as possible throughout the overlapped seam area, will produce avery good uniform black level throughout the image, including the seamarea. These knife edges block the image from the respective projectorsoutside of the overlap region, eliminating stray light that oftensurrounds images from most projection technologies. However, simplestraight knife edges introduce a luminance “ringing,” whereby the edgehas a slightly sinusoidal pattern to the decay from full luminance tosystem black. This “ringing” is generally attributed to artifactsarising from integrating bars utilized in projection system lamphouses,or from simple edge diffraction effects, and leads to an obvious linepattern along the seam visible in gray scale and peak white images.Other traditional methods of butt seaming or overlapping images havetypically failed to achieve sufficient precision in matching to make theseam truly invisible for a wide range of image content or projectiongeometries.

Therefore, techniques and equipment for blending multiple projectiondisplays to form a single display with solutions to the geometric andphotometric issues is desirable.

SUMMARY OF THE INVENTION

The present invention seeks to provide solutions to resolve thesegeometric and photometric issues and provide an invisible seam when twoor more sub-images are blended together to form a composite image. Itfurther does so in a more comprehensive manner than heretoforeconsidered, attempting to create equipment and techniques capable ofproviding images of sufficient overall quality that they may be used invenues instead of, or in addition to, traditional large-format filmprojectors without disturbing audience perception that the viewed imagesare of high quality. As noted above, this perception is a significantaspect of modern-day viewing experiences, at times helping determineoverall success among the public of particular motion pictures.

The present invention solves these problems optically by using maskswith complimentary, non-linear edges placed between the projection axisand a screen. In one embodiment the mask edges are a saw tooth shape.Many other complementary, non-linear edges are possible.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematized diagram of an exemplary system.

FIG. 2 is a schematized diagram of an exemplary mask.

FIG. 3 is a schematized depiction of a first sub-image tiled with asecond sub-image.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematized diagram of one possible embodiment ofthe present invention. As shown in FIG. 1, in this embodiment two SLMprojectors 1 and 2 are used. This invention could be applied to a widerange of projection technologies or be internalized inside a singleprojection system as an integrated package. The present invention couldalso be utilized with more than two projectors.

As shown in FIG. 1, projector 1 is positioned so that its projectionaxis projects just past a 45 degree front surface mirror 3. Projector 2is located orthogonally to projector 1 so that its projection axis isreflected off the front surface mirror 3. The image presented by theprojector 2 is electronically flipped, if necessary, using techniquesknown in the art. The arrangement of FIG. 1 allows the two projectors tohave near-coincident virtual projection points, without the losses andghost images caused when using a beam splitter mirror. This coincidenceis desirable in order to reduce the effects of screen gain. When theprojection points are not coincident the seam will be made more visibleby the difference in brightness across the screen since the reflectedlight from different projection points arrives at different points foroff axis observers.

Mask 6 is placed between lens 4 and a screen 9 so that the mask 6 edgeoverlaps slightly with the projection axis of projector 1. Similarly,mask 7 is placed between lens 5 and the mirror 3 so that its edgeoverlaps slightly with the projection axis of projector 2. As shown inFIG. 1, a sub-image 8 produced by projector 1 is displayed on a screen 9adjacent to a sub-image 10 produced by projector 2.

A beamsplitter could be used with the embodiment shown in FIG. 1. With abeam splitter it is possible to achieve perfect coincidence, buttypically a 50% or more light loss is experienced. The beam splitter ispositioned at the intersections of the light from projectors 1 and 2 sothat the light from projector 1 is transmitted by the beam splitter tothe screen, and the light from projector 2 is reflected through 90degrees to the screen. The masks for each lens remain in the locationsshown in FIG. 1.

The lens 4 of projector 1 and the lens 5 of projector 2 are horizontallyoffset or shifted (for a vertical seam) so that the seamed area of theimage falls within a narrow margin of the lens optical axis (generallyless than 5–10% of the format width), while the images themselves arefree of keystoning. This generally allows the virtual projection pointof the reflected image to be located near co-incidentally with the otherprojection point, within a very small fraction of the lens focal length,depending on projection angles, seam width desired, and lens parameterssuch as exit pupil size and location. (Typically, the axis of a lens ismost free of aberration, which, if present, could affect the visibilityof a seam.)

In another embodiment, two forward looking projectors (both lensesfacing directly to the screen) mounted so their lenses are as closetogether as possible could be used. Such an embodiment will producesufficiently accurate alignment (sub-pixel) on the screen to eliminatethe need for the mirror at least for geometric considerations.

Having achieved good geometric alignment of the images from twoprojectors, luminance and color space matching of the two projectors canbe achieved using techniques known in the art. Care and precision arenecessary to achieve required tolerances—with a wider blend areaallowing more relaxed tolerances. SLM based projectors in particularoffer very good stability and are very well suited to achieving therequired tight matching. SLM projectors are not a prerequisite for thesetechniques.

To alleviate the luminance ringing effect caused by using a knife edgedmask of the prior art; the present invention uses masks withcomplimentary but nonlinear edges in the optical path. FIG. 2 shows anexemplary embodiment of a mask. The mask may be made of metal andpainted with a flat black paint or otherwise treated to reducereflections. The use of masks such as shown in FIG. 2 produces a seriesof alternating diagonal seams, which although still containing the linepatterns or “ringing” of the prior art, are now broken up visually tothe point that even in peak white or grey scale images the seam isessentially invisible. FIG. 2 shows a mask with a simple zig-zag or sawtooth pattern, preferably with a frequency of 7–10 points across theseam. A multitude of other complimentary patterns such as sinusiodal oreven random patterns have proven successful. Color fringing orpatterning effects are also noted with the use of masks. These effectsare attributed in part to the axial chromatic aberrations present in theprojection lens. Since the mask is in an out of focus position withrespect to the image plane, rays of different color light may intersectthe mask at different points for a given field position for the mask.This contributes to a color “fringe.” In addition, DMD based projectorsdo not have completely uniform illumination of all colors, and thepresence of the mask may act to highlight these non-uniformities.

In one embodiment, the mask is placed as close to the outside of thelens pupil as possible with the non-linear edge of the mask along theoptical axis. However, the mask could be placed farther away from thelens pupil or could come before the lens.

FIG. 3 illustrates a schematized depiction of the blended image ofsub-image 8 and sub-image 10 on the screen 9. As shown in FIG. 3, maskswith complementary and non-linear edges in a saw tooth pattern are used.The overlap section 20 is depicted as in between the dotted lines 21 and22. The two sub-images 8 and 10 projected using the embodiment of FIG. 1are generally overlapped by about 5–10% of the format dimension at theseam, which means good sub-pixel geometric alignment must be maintainedover this region.

Further digital correction of the images presented to the projectorscould be used in conjunction with the present invention—such asintroducing negative “rings” into the images to offset the opticaleffects. A variety of digital processing techniques known in the art,such as using feedback imaging systems to measure luminance orgeometrical variations across seams and adjusting the imagesaccordingly, could be used for this purpose.

The foregoing is provided for purposes of illustrating, explaining, anddescribing embodiments of the present invention. Thus, furthermodifications and adaptations to these embodiments will be apparent tothose skilled in the art and may be made without departing from thescope or spirit of the invention. Yet, additionally ferroelectricdevices, liquid-crystal displays (LCD), self luminous array devices,laser scanning systems incorporating electro-optical orelectromechanical scanning devices, or other light sources or valves maybe employed as necessary or desired.

1. A projection system, comprising: at least one projection devicehaving a first lens and a second lens, the projection device projectinga first sub-image through the first lens and a second sub-image throughthe second lens; a screen for displaying the first sub-image and thesecond sub-image; a first mask positioned between the first lens and thescreen, the first mask having a first non-linear edge in an optical pathof the first sub-image creating a first non-linear image edge; and asecond mask positioned between the second lens and the screen, thesecond mask having a second non-linear edge, that is complimentary tothe first mask, in an optical path of the second sub-image creating asecond non-linear image edge complimentary to the first non-linear imageedge, wherein the first sub-image and second sub-image are combined onthe screen such that the first sub-image and the second sub-imageoverlap at the first non-linear image edge and the second non-linearimage edge to form a non-linear seam.
 2. The projection system of claim1 wherein the projection device is a spatial light modulator typeprojector.
 3. The projection system of claim 1 wherein the projectiondevice is a deformable mirror device type projector.
 4. The projectionsystem of claim 1 wherein the projection device is a liquid crystaldevice type projector.
 5. The projection system of claim 1 wherein theprojection device is a ferroelectric type projector.
 6. The projectionsystem of claim 1 wherein the projection device is a self luminous arraytype projector.
 7. The projection system of claim 1 wherein theprojection device is a laser scanning system type projector.
 8. Theprojection system of claim 1 wherein the first lens and the second lensfree the screen.
 9. The projection system of claim 1 wherein the firstnon-linear edge of the first mask is a first saw tooth pattern and thesecond non-linear edge of the second mask is a second saw toot pattern.10. The projection system of claim 9 wherein the first saw tooth patternhas a pattern of teeth formed from +45 degree and −45 degree lines andthe second saw tooth pattern has a pattern of teeth formed from +45degree and −45 degree lines.
 11. The projection system of claim 1wherein the first mask is positioned close to the first lens and thesecond mask is positioned close to the second lens.
 12. The projectionsystem of claim 1 wherein the sub-images are corrected digitally tooffset optical effects.
 13. A projection system, comprising: a firstprojection device having a first projection axis and including a firstlens having a lens axis, the first projection device projecting a firstsub-image through the first lens; a second projection device having asecond projection axis and including a second lens having a lens axis,the second projection device projecting a second sub-image through thesecond lens; a screen for displaying the first sub-image and the secondsub-image; a first mask positioned between the first lens and thescreen, the first mask having a first non-liner edge in the optical pathof the first sub-image creating a first non-linear image edge; and asecond mask positioned between the second lens and the screen, thesecond mask having a second non-linear edge, that is complimentary tothe first mask, in the optical path of the second sub-image creating asecond non-linear image edge complimentary to the first non-linear imageedge, wherein the first sub-image is adjacent to the second sub-image onthe screen such that the first sub-image and the second sub-imageoverlap at the first non-linear image edge and the second non-linearimage edge to form a non-linear seamed area.
 14. The projection systemof claim 13 wherein the first projection device and the secondprojection device are spatial light modulator type projectors.
 15. Theprojection system of claim 13 wherein the first projection device andthe second projection device are deformable mirror device typeprojectors.
 16. The projection system of claim 13 wherein the firstprojection device and the second projection device are liquid crystaldevice type projectors.
 17. The projection system of claim 13 whereinthe first projection device and the second projection device areferroelectric type projectors.
 18. The projection system of claim 13wherein the first projection device and the second projection device areself luminous array type projectors.
 19. The projection system of claim13 wherein the first projection device and the second projection deviceare laser scanning system type projectors.
 20. The projection system ofclaim 13 wherein the first projection device is offset from the secondprojection device so that the seamed area falls within a narrow marginof the first lean axis and the second lens axis.
 21. The projectionsystem of claim 13 wherein the first lens and the second lens face thescreen.
 22. The projection system of claim 13 wherein the firstprojection device and the second projection device have substantiallycoincident virtual projection points.
 23. The projection system of claim13 wherein the first mask overlaps the first projection axis of thefirst projection device and the second mask overlaps the secondprojection axis of the second projector.
 24. The projection system ofclaim 13 wherein the first non-linear edge of the first mask is a firstsaw tooth pattern and the second non-linear edge of the second mask is asecond saw tooth pattern.
 25. The projection system of claim 24 whereinthe first saw tooth pattern has a pattern of teeth formed from +45degree and −45 degree lines and the second saw tooth pattern has apattern of teeth formed from +45 degree and −45 degree lines.
 26. Theprojection system of claim 13 wherein the first projection axis of thefirst projection device is substantially perpendicular to the secondprojection axis of the second projection device and the projectionsystem further comprises a mirror for reflecting the second sub-image onthe screen.
 27. The projection system of claim 26 wherein the secondsub-image is electronically flipped.
 28. The projection system of claim13 wherein the first projection axis of the first projection device issubstantially perpendicular to the second projection axis of the secondprojection device and the projection system further comprises a beamsplitter positioned at the intersection of the first and secondprojection axes so that the first sub-image is transmitted to the screenand the second sub-image is reflected on to the screen.
 29. Theprojection system of claim 13 wherein the first mask is positioned closeto the first lens and the second mask is positioned close to the secondlens.
 30. The projection system of claim 13 wherein the sub-images arecorrected digitally to offset optical effects.